package main

import (
	"os"
	"path/filepath"
	"strings"
	"testing"

	"github.com/stretchr/testify/require"
)

func TestFreeLeafHoldsAShortMessageWordForWord(t *testing.T) {
	message := Message{
		ID:   7,
		Kind: "user",
		Text: strings.Repeat("a", nodeBytes-len("user: ")),
	}

	node, free := freeLeaf(message)
	require.True(t, free)
	require.Equal(t, Node{
		Level: 0,
		Index: 7,
		Text:  "user: " + message.Text,
		Size:  nodeBytes,
	}, node)

	message.Text += "a"
	_, free = freeLeaf(message)
	require.False(t, free)
}

func TestFreeMergeJoinsShortSiblings(t *testing.T) {
	left := testNode(1, 2, "left")
	right := testNode(1, 3, "right")

	node, free := freeMerge(left, right)
	require.True(t, free)
	require.Equal(t, testNode(2, 1, "left\nright"), node)

	right = testNode(1, 3, strings.Repeat("r", nodeBytes-len("left")))
	_, free = freeMerge(left, right)
	require.False(t, free)
}

func TestTreeBuildsEachNodeOnce(t *testing.T) {
	tree, err := openTree(t.Context(), t.TempDir(), 2, newTestClock().Now)
	require.NoError(t, err)

	defer func() {
		require.NoError(t, tree.Close())
	}()

	require.NoError(t, tree.Add(testNode(0, 0, "user: a")))
	require.ErrorContains(t, tree.Add(testNode(0, 0, "user: b")), "already built")
	require.ErrorContains(t, tree.Add(testNode(1, 0, "a b")), "child that is not built")

	require.NoError(t, tree.Add(testNode(0, 1, "reply: b")))
	require.NoError(t, tree.Add(testNode(1, 0, "a b")))

	require.Equal(t, "user: a", readNode(t, tree, 0, 0).Text)
}

func TestTreeReopenLoadsTheSameNodes(t *testing.T) {
	root := t.TempDir()
	clock := newTestClock()
	tree, err := openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	nodes := []Node{
		testNode(0, 1, "reply: b"),
		testNode(0, 0, "user: a"),
		testNode(1, 0, "user: a\nreply: b"),
	}
	for _, node := range nodes {
		require.NoError(t, tree.Add(node))
	}

	require.NoError(t, tree.Close())

	data, err := os.ReadFile(filepath.Join(root, "tree", "2026-01-01.jsonl"))
	require.NoError(t, err)
	require.Equal(t, `{"l":0,"i":1,"text":"reply: b","size":8}`+"\n", strings.SplitAfter(string(data), "\n")[0])

	tree, err = openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	defer func() {
		require.NoError(t, tree.Close())
	}()

	require.Equal(t, len(nodes), tree.Count())
	for _, node := range nodes {
		require.Equal(t, node, readNode(t, tree, node.Level, node.Index))
	}
}

func TestTreeBuildsAMissingIndexAgain(t *testing.T) {
	root := t.TempDir()
	clock := newTestClock()
	tree, err := openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	nodes := []Node{
		testNode(0, 1, "reply: b"),
		testNode(0, 0, "user: a"),
		testNode(1, 0, "user: a\nreply: b"),
	}
	for _, node := range nodes {
		require.NoError(t, tree.Add(node))
	}

	require.NoError(t, tree.Close())
	require.NoError(t, os.RemoveAll(filepath.Join(root, "index")))

	_, err = openTree(t.Context(), root, 1, clock.Now)
	require.ErrorContains(t, err, "covers messages after the log")
	require.NoError(t, os.RemoveAll(filepath.Join(root, "index")))

	tree, err = openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	defer func() {
		require.NoError(t, tree.Close())
	}()

	require.Equal(t, len(nodes), tree.Count())
	for _, node := range nodes {
		require.Equal(t, node, readNode(t, tree, node.Level, node.Index))
	}
}

func TestTreeIndexesTheNodesAfterACrash(t *testing.T) {
	root := t.TempDir()
	clock := newTestClock()
	tree, err := openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	require.NoError(t, tree.Add(testNode(0, 0, "user: a")))
	require.NoError(t, tree.Add(testNode(0, 1, "reply: b")))
	require.NoError(t, tree.Close())

	// A crash after the line write and in the middle of the index writes.
	order := filepath.Join(root, "index", "tree.idx")
	require.NoError(t, os.Truncate(order, treeRecordBytes+5))
	require.NoError(t, os.Truncate(filepath.Join(root, "index", "tree-0.idx"), positionBytes))

	tree, err = openTree(t.Context(), root, 2, clock.Now)
	require.NoError(t, err)

	defer func() {
		require.NoError(t, tree.Close())
	}()

	require.Equal(t, 2, tree.Count())
	require.Equal(t, "reply: b", readNode(t, tree, 0, 1).Text)
	require.NoError(t, tree.Add(testNode(1, 0, "user: a\nreply: b")))
}

// isBuilt tells if the node (l, i) of tree is built.
func isBuilt(t *testing.T, tree *Tree, level, index int) bool {
	t.Helper()

	built, err := tree.Built(level, index)
	require.NoError(t, err)

	return built
}

// readNode reads the node (l, i) of tree, which must be built.
func readNode(t *testing.T, tree *Tree, level, index int) Node {
	t.Helper()

	node, built, err := tree.Node(level, index)
	require.NoError(t, err)
	require.True(t, built, "node (%d, %d)", level, index)

	return node
}

func testNode(level, index int, text string) Node {
	return Node{
		Level: level,
		Index: index,
		Text:  text,
		Size:  len(text),
	}
}