package gigaparsec_test

import (
	"bytes"
	"io"
	"testing"

	"git.codemonkeysoftware.net/b/gigaparsec"
	ptest "git.codemonkeysoftware.net/b/gigaparsec/test"
	pgen "git.codemonkeysoftware.net/b/gigaparsec/test/generator"
	"github.com/shoenig/test"
	"github.com/shoenig/test/must"
	"pgregory.net/rapid"
)

func TestState(t *testing.T) {
	t.Run("state reads the same position every time", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
		dst := pgen.SliceOfNZero[byte](0, len(data)-1).Draw(t, "dst")
		expected := data[:len(dst)]
		st := gigaparsec.MakeState(bytes.NewReader(data))

		_, next, err := st.Read(dst)
		must.NoError(t, err)
		must.SliceEqOp(t, expected, dst)

		next.Read(dst)
		_, _, err = st.Read(dst)
		must.NoError(t, err)
		must.SliceEqOp(t, expected, dst)
	}))
	t.Run("Read returns io.EOF iff it overruns source", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
		dst := pgen.SliceOfNZero[byte](0, 200).Draw(t, "dst")
		st := gigaparsec.MakeState(bytes.NewReader(data))

		n, _, err := st.Read(dst)
		t.Logf("n=%d", n)
		must.EqOp(t, min(len(data), len(dst)), int(n))
		if len(dst) > len(data) || st.Pos() == uint64(len(data)) {
			must.ErrorIs(t, err, io.EOF)
		} else {
			must.NoError(t, err)
		}
	}))
	t.Run("next state reads next input", rapid.MakeCheck(func(t *rapid.T) {
		const maxLen = 100
		data := rapid.SliceOfN(rapid.Byte(), 1, maxLen).Draw(t, "data")
		skip := rapid.IntRange(0, len(data)-1).Draw(t, "skip")
		st := gigaparsec.MakeState(bytes.NewReader(data))

		_, next, err := st.Read(make([]byte, skip))
		must.NoError(t, err)
		must.EqOp(t, skip, int(next.Pos()))
		dst := make([]byte, maxLen)
		n, _, _ := next.Read(dst)
		must.SliceEqOp(t, data[skip:skip+int(n)], dst[:n])
	}))
	t.Run("Read returns io.EOF if n is less than requested", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 0, 100).Draw(t, "data")
		st := gigaparsec.MakeState(bytes.NewReader(data))

		n, _, err := st.Read(make([]byte, len(data)+1))
		test.ErrorIs(t, err, io.EOF)
		test.EqOp(t, len(data), int(n))
	}))
	t.Run("At sets state position", rapid.MakeCheck(func(t *rapid.T) {
		data := rapid.SliceOfN(rapid.Byte(), 1, 100).Draw(t, "data")
		pos := rapid.Uint64Range(0, uint64(len(data)-1)).Draw(t, "pos")
		st := gigaparsec.MakeState(bytes.NewReader(data)).At(pos)

		dst := make([]byte, 1)
		n, _, err := st.Read(dst)
		test.EqOp(t, 1, n)
		test.NoError(t, err)
		test.EqOp(t, data[pos], dst[0])
	}))
	t.Run("Pos returns correct position after At", rapid.MakeCheck(func(t *rapid.T) {
		var data []byte
		pos := rapid.Uint64().Draw(t, "pos")
		st := gigaparsec.MakeState(bytes.NewReader(data)).At(pos)
		test.EqOp(t, pos, st.Pos())
	}))
	t.Run("Pos returns correct position after Read", rapid.MakeCheck(func(t *rapid.T) {
		const maxLen = 100
		data := rapid.SliceOfN(rapid.Byte(), 1, maxLen).Draw(t, "data")
		skip := rapid.Uint64Range(0, uint64(len(data)-1)).Draw(t, "skip")
		st := gigaparsec.MakeState(bytes.NewReader(data))

		_, next, err := st.Read(make([]byte, skip))
		must.NoError(t, err)
		test.EqOp(t, skip, next.Pos())
	}))
	t.Run("Read returns an error if the ReaderAt fails", rapid.MakeCheck(func(t *rapid.T) {
		expectedErr := pgen.Error().Draw(t, "expectedErr")
		startPos := rapid.Uint64().Draw(t, "startPos")
		dst := pgen.SliceOfNZero[byte](0, 100).Draw(t, "dst")
		st := gigaparsec.MakeState(ptest.ErrReaderAt(expectedErr)).At(startPos)
		n, next, err := st.Read(dst)
		test.ErrorIs(t, err, expectedErr)
		test.EqOp(t, startPos, next.Pos())
		test.Zero(t, n)
	}))
}