package alias

import (
	"reflect"
	"testing"

	"gitea.maximumdirect.net/eric/CommandKit/internal/commandpath"
)

func TestResolverUsesLongestTokenPrefixAndPreservesSuffix(t *testing.T) {
	resolver, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"app", "collections"}},
	})
	if err != nil {
		t.Fatal(err)
	}

	got := resolver.Resolve(commandpath.Path{"list", "collections", "extra"})
	want := commandpath.Path{"app", "collections", "extra"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
	got = resolver.Resolve(commandpath.Path{"list", "prompts"})
	want = commandpath.Path{"promptkit", "list", "prompts"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
	reversed, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"app", "collections"}},
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
	})
	if err != nil {
		t.Fatal(err)
	}
	if got := reversed.Resolve(commandpath.Path{"list", "collections", "extra"}); !got.Equal(commandpath.Path{"app", "collections", "extra"}) {
		t.Fatalf("reverse-order Resolve() = %#v", got)
	}
}

func TestResolverFallsBackAfterLongerTokenMatchFails(t *testing.T) {
	resolver, err := NewResolver([]Mapping{
		{Source: commandpath.Path{"a"}, Target: commandpath.Path{"short"}},
		{Source: commandpath.Path{"a", "b", "c"}, Target: commandpath.Path{"long"}},
	})
	if err != nil {
		t.Fatal(err)
	}
	got := resolver.Resolve(commandpath.Path{"a", "b", "x"})
	want := commandpath.Path{"short", "b", "x"}
	if !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
}

func TestResolverDoesNotMatchUnknownTokens(t *testing.T) {
	resolver, err := NewResolver([]Mapping{{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}}})
	if err != nil {
		t.Fatal(err)
	}
	input := commandpath.Path{"listing", "collections"}
	got := resolver.Resolve(input)
	if !got.Equal(input) {
		t.Fatalf("Resolve() = %#v, want unchanged %#v", got, input)
	}
}

func TestCompiledMachineMatchesDirectResolver(t *testing.T) {
	mappings := []Mapping{
		{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"list", "collections"}, Target: commandpath.Path{"promptkit", "list", "collections"}},
		{Source: commandpath.Path{"pk"}, Target: commandpath.Path{"promptkit"}},
		{Source: commandpath.Path{"promptkit", "list", "bundles"}, Target: commandpath.Path{"promptkit", "list", "collections"}},
		{Source: commandpath.Path{"short"}, Target: commandpath.Path{"promptkit", "list"}},
		{Source: commandpath.Path{"short", "b", "c"}, Target: commandpath.Path{"long"}},
	}
	resolver, machine, err := Compile(mappings)
	if err != nil {
		t.Fatal(err)
	}
	for key, operation := range machine.transitions {
		if len(operation.push) > 2 {
			t.Fatalf("transition %+v pushes %d symbols", key, len(operation.push))
		}
	}
	cases := []commandpath.Path{
		{"list"},
		{"list", "prompts"},
		{"list", "collections"},
		{"list", "collections", "extra"},
		{"pk", "list", "bundles", "tail"},
		{"short", "b", "x"},
		{"unknown", "operand"},
		{},
	}
	for _, marker := range []symbolKind{endSymbol, boundarySymbol} {
		for _, input := range cases {
			t.Run(input.String(), func(t *testing.T) {
				got, err := runMachineForTest(machine, input, marker)
				if err != nil {
					t.Fatal(err)
				}
				want := expectedSymbols(machine, resolver.Resolve(input), marker)
				if !reflect.DeepEqual(got, want) {
					t.Fatalf("machine result = %#v, want direct result %#v", got, want)
				}
			})
		}
	}
}

func TestResolverTreatsIdenticalMappingsAsIdempotent(t *testing.T) {
	mapping := Mapping{Source: commandpath.Path{"list"}, Target: commandpath.Path{"promptkit", "list"}}
	resolver, err := NewResolver([]Mapping{mapping, mapping})
	if err != nil {
		t.Fatal(err)
	}
	got := resolver.Resolve(commandpath.Path{"list", "prompts"})
	if want := (commandpath.Path{"promptkit", "list", "prompts"}); !got.Equal(want) {
		t.Fatalf("Resolve() = %#v, want %#v", got, want)
	}
}

func TestResolverRejectsInvalidAndConflictingMappings(t *testing.T) {
	for name, mappings := range map[string][]Mapping{
		"empty source": {{Target: commandpath.Path{"target"}}},
		"empty target": {{Source: commandpath.Path{"source"}}},
		"conflicting target": {
			{Source: commandpath.Path{"source"}, Target: commandpath.Path{"first"}},
			{Source: commandpath.Path{"source"}, Target: commandpath.Path{"second"}},
		},
	} {
		t.Run(name, func(t *testing.T) {
			if _, err := NewResolver(mappings); err == nil {
				t.Fatal("NewResolver() succeeded")
			}
		})
	}
}

func expectedSymbols(machine *Machine, path commandpath.Path, marker symbolKind) []symbol {
	result := make([]symbol, 0, len(path)+1)
	for _, token := range path {
		result = append(result, machine.classify(token))
	}
	result = append(result, symbol{kind: marker})
	return result
}

func runMachineForTest(machine *Machine, input commandpath.Path, marker symbolKind) ([]symbol, error) {
	stack := expectedSymbols(machine, input, marker)
	control := machine.start
	for steps := 0; steps < 10000; steps++ {
		if control == machine.halt {
			return stack, nil
		}
		if len(stack) == 0 {
			return nil, errMachineStackEmpty
		}
		operation, ok := machine.transitions[transitionKey{control: control, read: stack[0]}]
		if !ok {
			return nil, errMachineTransitionMissing
		}
		stack = append(append([]symbol(nil), operation.push...), stack[1:]...)
		control = operation.next
	}
	return nil, errMachineTestDidNotHalt
}

var (
	errMachineStackEmpty        = testError("compiled machine emptied its stack")
	errMachineTransitionMissing = testError("compiled machine has no transition")
	errMachineTestDidNotHalt    = testError("compiled machine did not halt in the test interpreter")
)

type testError string

func (err testError) Error() string { return string(err) }

func (machine *Machine) classify(token string) symbol {
	if _, exists := machine.literals[token]; exists {
		return symbol{kind: literalSymbol, value: token}
	}
	return symbol{kind: otherSymbol}
}