/*
	testexec is a package that offers some helper functions for testing
	execution of commands (either with actual os.Exec, or a callback of your defining),
	and tests them using certain conventions of testmark dir+filename names for the fixture data.

	This package isn't part of testmark's core, nor is it particularly special.
	It's just some conventions that may be handy.
*/
package testexec

import (
	"bytes"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"testing"

	"github.com/warpfork/go-testmark"
)

// ExecFn is the outline for a callback that can run individual commands in a sequence of commands.
// An ExecFn can be placed in the Tester config struct to control the behavior of TestSequence.
//
// Semantically, an ExecFn is supposed to treat its args slice roughly as `os.StartProcess` treats `argv`:
// the zeroth element of the slice is the command name (or path), and subsequent slice elements are positional arguments to that command.
// However, it's a freeform callback: you can do as you wish.
type ExecFn func(args []string, stdin io.Reader, stdout, stderr io.Writer) (exitcode int, oshit error)

// ScriptFn is the outline for a callback that can run a script.
// A ScriptFn can be placed in the Tester config struct to control the behavior of TestScript.
//
// Semantically, ScriptFn is... quite free to do whatever it wishes.
// A typical implementation (and the default behavior of this package, if you don't supply a ScriptFn)
// is to handle the script as if it was a bash shell script (so, piping, env vars, etc, are all possible).
// However, one could place any kind of script parser and interpreter within this callback.
type ScriptFn func(script string, stdin io.Reader, stdout, stderr io.Writer) (exitcode int, oshit error)

// FilterFn is the outline for a callback that can be used to normalize some parts of output strings.
// A common example of this is to strip timestamps back out of log messages for a program that emits logs with timestamps.
type FilterFn func(line string) (replacement string)

// AssertFn can be used in Tester to specify a better test assertion function.
// For example, if you use the quicktest package, this is an excellent snippet which will result in good diffs:
//
//		func(...) { quicktest.Assert(t, actual, quicktest.CmpEquals(), expect) }
//
// The default behavior, if a Tester object doesn't get an AssertFn, is to fall back to a very basic call to `t.Errorf`.
type AssertFn func(t *testing.T, actual, expect string)

// Tester is a configuration-gathering structure.
// Each of the `Test*` methods upon it will use these callbacks to define their behavior.
//
// All of the fields can be nil, which will result in default behaviors.
// (A nil ExecFn will result in an OS exec being used (specifically: `ExecFn_Exec`);
// a nil FilterFn means no filtering will occur;
// a nil AssertFn means a very basic check using t.Errorf will be used.)
//
// The 'Patches' accumulator will be used to gather new fixture data if `testmark.Regen` is true.
// (If the pointer is nil, a warning will be logged.)
// It is the user's responsibility to actually apply the patches and save the updated document.
type Tester struct {
	ExecFn
	ScriptFn
	FilterFn
	AssertFn

	Patches *testmark.PatchAccumulator
}

func (tcfg *Tester) init() {
	if tcfg.ExecFn == nil {
		tcfg.ExecFn = ExecFn_Exec
	}
	if tcfg.ScriptFn == nil {
		tcfg.ScriptFn = ScriptFn_ExecBash
	}
	if tcfg.AssertFn == nil {
		tcfg.AssertFn = defaultAssertFn
	}
}

// TestSequence runs a test based on a "sequence" instruction -- a hunk called "sequence" should have a series of lines,
// and each line is a command to be executed.
//
// The model of execution and model of environment used is very simple:
// it's just consecutive lines which will be fed one after another to an ExecFn.
// There is *not* a scripting engine involved (you can't "pipe", use "env vars", use "subcommands",
// "$?" has no special meaning, etc; there's no shell interpreting those things).
// (The ExecFn can be as simple or as complex as you want, of course -- but none of these features are provided for you.)
//
// The parser that splits up each line of the sequences into the args string slice is primitive.  It's simply whitespace splitting.
// If you need to test the handling of arguments that involve whitespace, there are two options:
// One, you may want to use TestScript instead (this will let you parse it yourself, and or just hand off to a shell of some kind which means you can use the shell's quoting rules);
// or, Two, you can change your sequence hunk name to `sequences.jsonl`, and put a json list on each line, which will be parsed and that list becomes the args.
//
// Each DirEnt can also contain several other named entries which will be treated specially.
// "output" -- if present, will cause the commands to be given a unified stdout and stderr buffer, and it will be checked against this data when done.
// "stdout" -- if present, works like "output", but only collects stdout.  Cannot be combined with "output".
// "stderr" -- ditto "stdout", but for (you guessed it) stderr.
// "exitcode" -- if present, should contains a base-10 number for the expected exit code.  If not present, an exitcode of 0 will be expected.
//
// Not every data DirEnt has to contain any of "output", "stdout", "stderr", or "exitcode".
// Containing none of them means the commands in the sequence will all be run,
// and the exitcode is expected to be zero from each,
// and nothing about their stdout nor stderr will be checked.
// (If you want to mandate that their output is empty, you must create a blank data block to say so explicitly.)
//
// Additionally, the commands can be run within a temp directory, with some files pre-populated,
// by use of data hunks under the "fs/" name.  So, "fs/foo.bar" will result in a file named "foo.bar" in the temp directory.
// The temp directory is applied by using `os.Chdir`, and so is not safe for use with concurrent tests.
// There are no special faculties for making empty directories, symlinks, setting file properties, etc;
// if you need to do anything fancy, a setup script may be a good direction to pursue.
//
// If you wish to run some commands, and gather and test (or ignore!) their output as one block,
// then run additional commands in a subtest, you can use another special path name
// in the testmark.DirEnt for that: `then-(.*)`.
// Anything starting with "then-" will cause a new nested `t.Run` block,
// which will have a name that is the rest of the path name once the "then-" prefix has been stripped.
// Inside that DirEnt, all the same rules apply again (we'll look for a "sequence" hunk, etc).
//
// Note that there are no faculties to expect a specific exitcode from a specific line of the sequence,
// nor are their faculties to extract outputs from one specific line of the sequence.
// If you are wanting to do these things, you can use the "then-" feature.
// (This is probably a nudge towards writing better documentation anyway:
// if you have a whole series of commands and it's a very specific one that should stand out,
// you should probably give it separate data blocks for sheer human readability anyway.)
//
// There is no faculty for ignoring an exitcode.
// Surely the systems you're so rigorously ensuring the quality of don't have nondeterministic exit codes;
// so why would you need to do this?  If it's allowed to be anything but zero, it should be expected to be that; and if it's expected, say so.
//
// This test system comes complete with fixture regeneration support.
// If `testmark.Regen` is true (e.g. you have invoked "go test" with the argument "-testmark.regen"),
// then instead of making any assertions, this function will accumulate patches
// in the `Tester.Patches` slice.
// Regen mode will only update hunks that already exist; it won't add them.
// As an edge case, note that if that an exitcode hunk is absent, but a nonzero exitcode is encountered,
// the test will still be failed, even though in patch regen mode most assertions are usually skipped.
func (tcfg Tester) TestSequence(t *testing.T, data testmark.DirEnt) {
	t.Helper()
	tcfg.test(t, data, true, false)
}

func (tcfg Tester) TestScript(t *testing.T, data testmark.DirEnt) {
	t.Helper()
	tcfg.test(t, data, false, true)
}

func (tcfg Tester) Test(t *testing.T, data testmark.DirEnt) {
	t.Helper()
	tcfg.test(t, data, true, true)
}

func (tcfg Tester) test(t *testing.T, data testmark.DirEnt, allowExec, allowScript bool) {
	t.Helper()
	tcfg.init()

	sequenceHunk, sequenceMode := data.Children["sequence"]
	scriptHunk, scriptMode := data.Children["script"]
	if !sequenceMode && !scriptMode {
		return
	}
	if sequenceMode && scriptMode {
		t.Logf("warning: dir %q contained both a 'script' and a 'sequence' hunk, which is nonsensical", data.Name)
		t.SkipNow()
	}
	if sequenceMode && !allowExec {
		t.Skipf("found sequence hunk but the test framework was invoked without permission to run those")
	}
	if scriptMode && !allowScript {
		t.Skipf("found sequence hunk but the test framework was invoked without permission to run those")
	}
	if *testmark.Regen && tcfg.Patches == nil {
		t.Logf("warning: testmark.regen mode engaged, but there is no patch accumulator available here")
		t.Skipf("nothing to do if requested to regenerate test fixtures but have nowhere to put data")
	}

	// Create a tempdir, and fill it with any files.
	if fsEnt, exists := data.Children["fs"]; exists {
		// Create and get into a tempdir.
		dir, err := ioutil.TempDir("", "testmarkexec")
		if err != nil {
			t.Errorf("test aborted: could not create tempdir: %s", err)
		}
		defer os.RemoveAll(dir)
		retreat, err := os.Getwd()
		if err != nil {
			t.Errorf("test aborted: could not find cwd: %s", err)
		}
		defer os.Chdir(retreat)
		if err := os.Chdir(dir); err != nil {
			t.Errorf("test aborted: could not chdir to tempdir: %s", err)
		}

		// Create files.
		if err := createFiles(fsEnt, "."); err != nil {
			t.Errorf("test aborted: could not populate files to tempdir: %s", err)
		}
	}

	// Prepare output buffers.
	var stdout, stderr io.Writer
	if _, exists := data.Children["output"]; exists {
		stdout = &bytes.Buffer{}
		stderr = stdout
		if _, exists := data.Children["stdout"]; exists {
			t.Errorf("testexec entry %q shouldn't contain 'stdout' hunk if it also specifies a unified 'output' hunk", data.Name)
		}
		if _, exists := data.Children["stderr"]; exists {
			t.Errorf("testexec entry %q shouldn't contain 'stderr' hunk if it also specifies a unified 'output' hunk", data.Name)
		}
	}
	if _, exists := data.Children["stdout"]; exists {
		stdout = &bytes.Buffer{}
	}
	if _, exists := data.Children["stderr"]; exists {
		stderr = &bytes.Buffer{}
	}
	var exitcode int

	// Do the thing.
	switch {
	case sequenceMode:
		exitcode = tcfg.doSequence(t, sequenceHunk.Hunk, stdout, stderr)
	case scriptMode:
		exitcode = tcfg.doScript(t, scriptHunk.Hunk, stdout, stderr)
	}

	// Okay, comparisons time.
	// Or, regen time!
	if ent, exists := data.Children["output"]; exists {
		bs := stdout.(*bytes.Buffer).Bytes()
		if *testmark.Regen {
			tcfg.Patches.AppendPatchIfBodyDiffers(*ent.Hunk, bs)
		} else {
			t.Run("check-combined-output", func(t *testing.T) {
				tcfg.AssertFn(t, string(bs), string(ent.Hunk.Body))
			})
		}
	}
	if ent, exists := data.Children["stdout"]; exists {
		bs := stdout.(*bytes.Buffer).Bytes()
		if *testmark.Regen {
			tcfg.Patches.AppendPatchIfBodyDiffers(*ent.Hunk, bs)
		} else {
			t.Run("check-stdout", func(t *testing.T) {
				tcfg.AssertFn(t, string(bs), string(ent.Hunk.Body))
			})
		}
	}
	if ent, exists := data.Children["stderr"]; exists {
		bs := stderr.(*bytes.Buffer).Bytes()
		if *testmark.Regen {
			tcfg.Patches.AppendPatchIfBodyDiffers(*ent.Hunk, bs)
		} else {
			t.Run("check-stderr", func(t *testing.T) {
				tcfg.AssertFn(t, string(bs), string(ent.Hunk.Body))
			})
		}
	}
	t.Run("check-exitcode", func(t *testing.T) {
		if ent, exists := data.Children["exitcode"]; exists {
			if *testmark.Regen {
				tcfg.Patches.AppendPatchIfBodyDiffers(*ent.Hunk, []byte(strconv.Itoa(exitcode)))
			} else {
				tcfg.AssertFn(t, strconv.Itoa(exitcode), strings.TrimSpace(string(ent.Hunk.Body)))
			}
		} else {
			tcfg.AssertFn(t, strconv.Itoa(exitcode), "0")
		}
	})

	// TODO: look for "then-*" dirs.

}

func (tcfg Tester) doSequence(t *testing.T, hunk *testmark.Hunk, stdout, stderr io.Writer) (exitcode int) {
	t.Helper()
	// Loop over the lines in the sequence.
	lines := bytes.Split(hunk.Body, []byte{'\n'})
	for _, line := range lines {
		args := strings.Fields(string(line))
		if len(args) < 1 {
			continue
		}

		var err error
		exitcode, err = tcfg.ExecFn(args, bytes.NewReader(nil), stdout, stderr)
		if err != nil {
			t.Fatalf("execution failed: error from ExecFn is %q", err)
		}
		if exitcode != 0 {
			break // TODO: it's probably still an error if that happens before the end?
		}
	}
	return
}

func (tcfg Tester) doScript(t *testing.T, hunk *testmark.Hunk, stdout, stderr io.Writer) (exitcode int) {
	t.Helper()
	var err error
	exitcode, err = tcfg.ScriptFn(string(hunk.Body), bytes.NewReader(nil), stdout, stderr)
	if err != nil {
		t.Fatalf("execution failed: error from script is %q", err)
	}
	return
}

// createFiles makes files and directories matching testmark hunks.
// It creates them relative to the os cwd plus prefix -- use with care.
func createFiles(dir *testmark.DirEnt, prefix string) error {
	if dir.Hunk != nil {
		return ioutil.WriteFile(prefix, dir.Hunk.Body, 0644)
	} else {
		if err := os.MkdirAll(prefix, 0755); err != nil {
			return err
		}
	}
	for _, ent := range dir.Children {
		if err := createFiles(ent, filepath.Join(prefix, ent.Name)); err != nil {
			return err
		}
	}
	return nil
}